Lithium-2,2,6,6-tetramethylpiperidide

The carbanion 5, formed from V,V-diethyl-5-phenyl-3//-azepin-2-amine (4) with potassium amide in liquid ammonia, or with lithium 2,2,6,6-tetramethylpiperidide in tetrahydrofuran, is thiolated by dialkyl or diaryl disulfides to yield 3-(alkylsulfanyl)-3//-azepines, e.g. 6.38... 

A more detailed investigation of the reaction reveals that alkylations with 2-halopropanes yield 1 4.5 mixtures of the 3- and 5-isopropyl-3//-azepines 20 and 21.224 The ratio of the two isomers is dependent on temperature and the deprotonating system. For example, with lithium 2,2.6,6-tetramethylpiperidide in tetrahydrofuran at 20 C a 1 1 mixture (20/21) is obtained, whereas at — 70 "C the ratio is 10 1. 

Lithium cyclohexylisopropylamide Lithium diisopropylamide Lithium hexamethyl disilazide Lithium 2,2,6,6-tetramethylpiperidide Methylaluminum I ij-(4-bromo-2,6-di-tert-butylphenoxide) I (s-(2,6-di-t-butyl-4-methylphenoxy)methyl aluminum mefa-Chloroperoxybenzoic acid Methyl... 

The easily obtainable 1,2-dihydro-2-boranaphthalene 27 can be depro-tonated by lithium 2,2,6,6-tetramethylpiperidide (LiTMP) to give the 2-boratanaphthalene 28, characterized via its derivative 29 (Scheme 5) (26). 

Ethyl 1-naphthylacetate 1-Naphthaleneacetic acid, ethyl ester (8,9) (2122-70-5) Lithium 2,2,6,6-tetramethylpiperidide Piperidine, 2,2,6,6-tetramethyl-, lithium salt (9) (38227-87-1)... 

The formation of tluorinated Q -hydroxy-jS-imino esters (180) by treatment of fluorinated imino ethers (179) with lithium 2,2,6,6-tetramethylpiperidide has been reported. A possible explanation for this interesting intramolecular rearrangement is proposed in Scheme 64. Acyclic imides derived from primary benzylic amines and amino acid esters have been found to undergo a novel nitrogen to carbon acyl migration via a base-generated carbanion to yield the corresponding a-amino... 

The metallation, especially the lithiation, of pyridazines, mentioned briefly in CHEC-II(1996) <1996CHEC-11(6)1 >, has been developed extensively since 1995 by Queguiner and co-workers for the derivatization of pyridazines and benzopyridazines. The bases of choice are usually lithium 2,2,6,6-tetramethylpiperidide (LTMP) and lithium diisopropylamide (EDA). Special efforts have been made to achieve regioselective lithiations. 

Since the first reports23 in 1963 on metalation of imines, a number of bases such as ethyl-1 or isopropylmagnesium bromide1 24, lithium9 and potassium diethylamide13, lithium diisopropyl-amide (LDA), lithium 2,2,6,6-tetramethylpiperidide (LTMP)9 10,13, and lithium bis(trimethylsi-lyl)amide13 have been successfully applied in the preparation of imine-derived azaenolates. The most common of these reagents is LDA which has been applied in deprotonation reactions of the whole palette of different imines. 

Thus, starting from the (—)-(S )-a-(methoxymethyl)benzeneethanaminc derived imines at low temperatures, (S )-2-methylcycloalkanones are obtained via the -azaenolates, whereas (R)-configurated products are obtained via the thermodynamically more stable Z-azaenolates by refluxing the anion solutions prior to alkylation. However, a high degree of enantiomeric excess is obtained only under thermodynamic conditions, presumably due to different selectives in the alkylation step (see Table 3). Variation of the base (/ert-butyllithium, lithium diethylamide, lithium 2,2,6,6-tetramethylpiperidide) and additives (hexamethylphosphoric triamide) did not improve the EjZ ratio (enantiomeric excess) significantly9. 

Aldehyde imines derived from alkoxyamines are metalated by LDA (0 °C, TIIF, 1 h6 or —23 °C, THF, 0.5 h13) and by potassium diethylamide, lithium bis(trimethylsily])amide and lithium 2,2,6,6-tetramethylpiperidide (—23 °C, THF, 2-4 h)1J. Nucleophilic bases such as alkyl- and aryllithium derivatives and, in some cases, alkylmagnesium bromides add to aldehyde imines. Best enantioselectivities are achieved with lithium 2,2,6,6-tetramethylpiperidide (LTMP)13. The... 

Although the regioselectivity of the alkylation reaction is independent of the nature and the steric bulk of the electrophile, it is dependent on the steric bulk of the base used for deprotonation. Lithium diisopropylamide (LDA) is superior for endo deprotonation, whereas exo dcprotonation is best achieved with the sterically hindered lithium 2,2,6,6-tetramethylpiperidide (LTMP)11,16. 

Since the reaction between methyllithium and 2,2,6,6-tetramethylpiperidine is relatively slow at lower temperatures, lithium 2,2,6,6-tetramethylpiperidide is best prepared at room temperature. The reagent may, however, be used over a wide range of temperatures. 

Preparation of Cyclopropanes from Alkyl Halides. Alkenes, and Lithium 2,2,6,6-Tetramethylpiperidide... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

As can be seen in the Table, lithium diisopropyl amide (IDA) is a satisfactory hase in cases where the carbon group (R) of a methyl ketone (RCOCH3) either is bulky or does not contain an a-roethylene or a-methine group. In the other cases, LDA is relatively ineffective. In such cases, however, the use of lithium 2,2,6,6-tetramethylpiperidide (LTMP) in place of LDA gives satisfactory results. The LTMP procedure appears to be the only documented method that is satisfactory for the conversion of the above-mentioned type. 

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